import java.io.BufferedReader import java.io.InputStream import java.io.InputStreamReader import java.lang.AssertionError import java.util.* import kotlin.math.abs import kotlin.math.max import kotlin.math.min val MOD = 1_000_000_007 class Solver(stream: InputStream, private val out: java.io.PrintWriter) { private val reader = BufferedReader(InputStreamReader(stream), 32768) fun solve() { val (L, R) = na(2) val MAX = 2*R + 100 val flg = BooleanArray(MAX + 1){true} val primes = mutableListOf() flg[0] = false flg[1] = false for (i in 2 ..MAX) { if (!flg[i]) continue primes += i var j = i * 2 while (j <= MAX) { flg[j] = false j += i } } /** * R^2 までの数値を判定できる */ fun isPrime(a: Int): Boolean { for (p in primes) { if (a <= p) return true if (a % p == 0) return false } return true } var ans = 0L for (a in L .. R) { run { // a-b = 1 val b = a - 1 if (b + 1 in (L..R)) { val x = a + b + 1 if (x % 2 == 0 && flg[x / 2]) ans++ } } run { // a - b = 2 val b = a - 2 if (b + 1 in (L..R)) { val x = a + b + 1 if (flg[x]) ans++ } } } out.println(ans) } private val isDebug = try { // なんか本番でエラーでる System.getenv("MY_DEBUG") != null } catch (t: Throwable) { false } private var tokenizer: StringTokenizer? = null private fun next(): String { while (tokenizer == null || !tokenizer!!.hasMoreTokens()) { tokenizer = StringTokenizer(reader.readLine()) } return tokenizer!!.nextToken() } private fun ni() = next().toInt() private fun nl() = next().toLong() private fun ns() = next() private fun na(n: Int, offset: Int = 0): IntArray { return IntArray(n) { ni() + offset } } private fun nal(n: Int, offset: Int = 0): LongArray { val res = LongArray(n) for (i in 0 until n) { res[i] = nl() + offset } return res } private fun na2(n: Int, offset: Int = 0): Array { val a = Array(2){IntArray(n)} for (i in 0 until n) { for (e in a) { e[i] = ni() + offset } } return a } private inline fun debug(msg: () -> String) { if (isDebug) System.err.println(msg()) } /** * コーナーケースでエラー出たりするので、debug(dp[1])のように添え字付きの場合はdebug{}をつかうこと */ private inline fun debug(a: LongArray) { debug { a.joinToString(" ") } } private inline fun debug(a: IntArray) { debug { a.joinToString(" ") } } private inline fun debug(a: BooleanArray) { debug { toString(a) } } private inline fun toString(a: BooleanArray) = run{a.map { if (it) 1 else 0 }.joinToString("")} private inline fun debugDim(A: Array) { if (isDebug) { for (a in A) { debug(a) } } } private inline fun debugDim(A: Array) { if (isDebug) { for (a in A) { debug(a) } } } private inline fun debugDim(A: Array) { if (isDebug) { for (a in A) { debug(a) } } } /** * 勝手にimport消されるのを防ぎたい */ private fun hoge() { min(1, 2) max(1, 2) abs(-10) } private inline fun assert(b: Boolean) = run{if (!b) throw AssertionError()} private inline fun assert(b: Boolean, f: () -> String) = run{if (!b) throw AssertionError(f())} companion object { // TestRunnerから呼びたいので単純なmainじゃだめ fun main() { val out = java.io.PrintWriter(System.out) Solver(System.`in`, out).solve() out.flush() } } } /** * judgeから呼ばれる */ fun main() = Solver.main()